Table of Contents 2001

We supplied concrete for a large floor, which the concrete contractor placed using a laser-guided self-propelled screed and riding power trowels. He initially floated the surface with pans and then used combo blades for later floating and troweling. During the late troweling stages, the blades were...

We are concerned about the temperature of our concrete exceeding acceptable limits (ACI or customer specifications). Are there any good strategies for dealing with this if one approach doesnÆt work in every situation?

I have a further question regarding the rounding of compressive strength results (ôHow Precisely Should Labs Round off Compressive Strength Results?ö April, page 26).At our lab, we test 4x8-inch and 6x8-inch concrete cylinders for compressive strength, and we round to the nearest 10 psi according...

Is there a screen setup for a wash plant that will take shale out more efficiently but at the same time retain the #50s and #100s? If a vibratory screen is the most efficient choice, should we add another type of equipment to our processing stream to remove the shale particles?

WeÆre just developing our mix designs for a project specifying lightweight aggregate. How long must we presoak the material to be sure that itÆs achieved full saturation? Since this project might continue into the late fall, when we commonly experience freezing temperatures, is it permissible to...

We had some cores drilled in a pavement section where there was some question about compressive strength. We got the compressive strength report back from the lab, and the strength was rounded to the nearest 1 psi. Is this correct?

We recently supplied a house slab where the bleedwater had a greenish tint. We discovered that the water retention pond we used for water collection had green algae that had formed on the surface and was used for concrete production. The concrete met and gained strength normally, however. Is there...

We were supplying a slab on grade with ordinary 3000-psi concrete when a section of the slab flash set or possibly false set; we are not sure. What is the difference between the two? The contractor asked us if he should retemper the area with water or finish it. What should we have suggested to the...

Recently, a local storeowner phoned our dispatcher to complain about the poor concrete he recently purchased for his exterior sidewalk. His complaint was that the surface was unduly rough and blotchy. When we investigated the complaint, we determined that the storeowner had purchased the concrete...